Expression and Roles of Teneurins in Zebrafish

Differential Expression Analysis Identifies Candidate Synaptogenic Molecules for Wiring Direction-Selective Circuits in the Retina

An organizational feature of neural circuits is the specificity of synaptic connections. A striking example is the direction-selective (DS) circuit of the retina. There are multiple subtypes of DS retinal ganglion cells (DSGCs) that prefer motion along one of four preferred directions. This computation is mediated by selective wiring of a single inhibitory interneuron, the starburst amacrine cell (SAC), with each DSGC subtype preferentially receiving input from a subset of SAC processes. We hypothesize that the molecular basis of this wiring is mediated in part by unique expression profiles of DSGC subtypes. To test this, we first performed paired recordings from isolated mouse retinas of both sexes to determine that postnatal day 10 (P10) represents the age at which asymmetric synapses form. Second, we performed RNA sequencing and differential expression analysis on isolated P10 ON-OFF DSGCs tuned for either nasal or ventral motion and identified candidates which may promote direction-specific wiring. We then used a conditional knock-out strategy to test the role of one candidate, the secreted synaptic organizer cerebellin-4 (Cbln4), in the development of DS tuning. Using two-photon calcium imaging, we observed a small deficit in directional tuning among ventral-preferring DSGCs lacking Cbln4, though whole-cell voltage-clamp recordings did not identify a significant change in inhibitory inputs. This suggests that Cbln4 does not function primarily via a cell-autonomous mechanism to instruct wiring of DS circuits. Nevertheless, our transcriptomic analysis identified unique candidate factors for gaining insights into the molecular mechanisms that instruct wiring specificity in the DS circuit.

Alternative splicing controls teneurin-3 compact dimer formation for neuronal recognition

Neuronal network formation is facilitated by recognition between synaptic cell adhesion molecules at the cell surface. Alternative splicing of cell adhesion molecules provides additional specificity in forming neuronal connections. For the teneurin family of cell adhesion molecules, alternative splicing of the EGF-repeats and NHL domain controls synaptic protein-protein interactions. Here we present cryo-EM structures of the compact dimeric ectodomain of two teneurin-3 isoforms that harbour the splice insert in the EGF-repeats. This dimer is stabilised by an EGF8-ABD contact between subunits. Cryo-EM reconstructions of all four splice variants, together with SAXS and negative stain EM, reveal compacted dimers for each, with variant-specific dimeric arrangements. This results in specific trans-cellular interactions, as tested in cell clustering and stripe assays. The compact conformations provide a structural basis for teneurin homo- and heterophilic interactions. Altogether, our findings demonstrate how alternative splicing results in rearrangements of the dimeric subunits, influencing neuronal recognition and likely circuit wiring.

Exome sequencing identifies ADGRG4 G-protein-coupled receptors gene as a novel cancer biomarker in ovarian cancer patients from North India

Adhesion G protein-coupled receptor G4 (ADGRG4) is a G protein-coupled receptor (GPCR) that belongs to the adhesion family. Participation of ADGRG4 in cell adhesion and migration, signaling pathway activation, influence on angiogenesis, and modulation of immune responses are some of the possible ways through which it may contribute to oncogenesis. Conducting extensive omics studies poses budgetary challenges to small labs in peripheral areas, primarily due to restricted research funding and resource limitations. Here we propose a low-budget model for biomarker screening. A total of 11 ovarian cancer samples were sent for exome sequencing. Among various genes, ADGRG4 variants were present in all 11 samples and thus were chosen as a potential biomarker in the present population. However, the precise role of ADGRG4 in cancer is not fully understood. The present study aims to look at the association between the ADGRG4 gene variants and their risk of ovarian cancer in the North Indian region of Jammu and Kashmir, India. Overall, 235 individuals (115 cases and 120 healthy controls) were genotyped for the selected biomarker using Sanger sequencing. Logistic regression was used to assess the relationship between the variant and ovarian cancer. A statistically significant association was identified between the ADGRG4 variant rs5930932 polymorphism and the incidence of ovarian cancer among the study population. When corrected for age and BMI, the dominating OR of variant rs5930932 was 1.035 (1.003-1.069) under HWE patients (0.95) and controls (0.18), with a p-value of (0.03). According to the findings of the current investigation, the ADGRG4 gene variant rs5930932 increases the chance of developing ovarian cancer in the studied population.

Embryonic and larval exposure to propylparaben induces developmental and long-term neurotoxicity in zebrafish model

Parabens are preservatives found in cosmetics, processed foods, and medications. The harmful repercussions on the central nervous system by one of the most common parabens, propylparaben (PrP), are yet unknown, especially during development. In this study, the neurodevelopmental effects of PrP and long-term neurotoxicity were investigated in the zebrafish model, using an integrated approach. Zebrafish embryos were exposed to two different concentrations of PrP (10 and 1000 μg/L), then larvae were examined for their behavioral phenotypes (open-field behavior, startle response, and circadian rhythmicity) and relevant brain markers (cyp19a1b, pax6a, shank3a, and gad1b). Long-term behavioral and cognitive impacts on sociability, cerebral functional asymmetry and thigmotaxis were also examined on juveniles at 30 dpf and 60 dpf. Moreover, proteomics and gene expression analysis were assessed in brains of 60 dpf zebrafish. Interestingly, thigmotaxis was decreased by the high dose in larvae and increased by the low dose in juveniles. The expression of shank3a and gad1b genes was repressed by both PrP concentrations pointing to possible effects of PrP on neurodevelopment and synaptogenesis. Proteomics analysis evidenced alterations related to brain development and lipid metabolism. Overall, the results demonstrated that early-life exposure to PrP promotes developmental and persistent neurobehavioral alterations in the zebrafish model, affecting genes and protein levels possibly associated with brain diseases.

Teneurin trans-axonal signaling prunes topographically missorted axons

Building precise neural circuits necessitates the elimination of axonal projections that have inaccurately formed during development. Although axonal pruning is a selective process, how it is initiated and controlled in vivo remains unclear. Here, we show that trans-axonal signaling mediated by the cell surface molecules Glypican-3, Teneurin-3, and Latrophilin-3 prunes misrouted retinal axons in the visual system. Retinotopic neuron transplantations revealed that pioneer ventral axons that elongate first along the optic tract instruct the pruning of dorsal axons that missort in that region. Glypican-3 and Teneurin-3 are both selectively expressed by ventral retinal ganglion cells and cooperate for correcting missorted dorsal axons. The adhesion G-protein-coupled receptor Latrophilin-3 signals along dorsal axons to initiate the elimination of topographic sorting errors. Altogether, our findings show an essential function for Glypican-3, Teneurin-3, and Latrophilin-3 in topographic tract organization and demonstrate that axonal pruning can be initiated by signaling among axons themselves.

Teneurin paralogues are able to localise synaptic sites driven by the intracellular domain and have the potential to form cis-heterodimers

Synaptic specificity during neurodevelopment is driven by combinatorial interactions between select cell adhesion molecules expressed at the synaptic membrane. These protein-protein interactions are important for instructing the correct connectivity and functionality of the nervous system. Teneurins are one family of synaptic adhesion molecules, highly conserved and widely expressed across interconnected areas during development. These type-II transmembrane glycoproteins are involved in regulating key neurodevelopmental processes during the establishment of neural connectivity. While four teneurin paralogues are found in vertebrates, their subcellular distribution within neurons and interaction between these different paralogues remains largely unexplored. Here we show, through fluorescently tagging teneurin paralogues, that true to their function as synaptic adhesion molecules, all four paralogues are found in a punctate manner and partially localised to synapses when overexpressed in neurons in vitro. Interestingly, each paralogue is differentially distributed across different pre- and post-synaptic sites. In organotypic cultures, Tenm3 is similarly localised to dendritic spines in CA1 neurons, particularly to spine attachment points. Furthermore, we show that the intracellular domain of teneurin plays an important role for synaptic localisation. Finally, while previous studies have shown that the extracellular domain of teneurins allows for active dimer formation and transsynaptic interactions, we find that all paralogues are able to form the full complement of homodimers and cis-heterodimers. This suggests that the combinatorial power to generate distinct molecular teneurin complexes underlying synaptic specificity is even higher than previously thought. The emerging link between teneurin with cancers and neurological disorders only serves to emphasise the importance of further elucidating the molecular mechanisms of teneurin function and their relation to human health and disease.

GATA4/5/6 family transcription factors are conserved determinants of cardiac versus pharyngeal mesoderm fate

GATA4/5/6 transcription factors play essential, conserved roles in heart development. To understand how GATA4/5/6 modulates the mesoderm-to-cardiac fate transition, we labeled, isolated, and performed single-cell gene expression analysis on cells that express gata5 at precardiac time points spanning zebrafish gastrulation to somitogenesis. We found that most mesendoderm-derived lineages had dynamic gata5/6 expression. In the absence of Gata5/6, the population structure of mesendoderm-derived cells was substantially altered. In addition to the expected absence of cardiac mesoderm, we confirmed a concomitant expansion of cranial-pharyngeal mesoderm. Moreover, Gata5/6 loss led to extensive changes in chromatin accessibility near cardiac and pharyngeal genes. Functional analyses in zebrafish and the tunicate Ciona, which has a single GATA4/5/6 homolog, revealed that GATA4/5/6 acts upstream of tbx1 to exert essential and cell-autonomous roles in promoting cardiac and inhibiting pharyngeal mesoderm identity. Overall, cardiac and pharyngeal mesoderm fate choices are achieved through an evolutionarily conserved GATA4/5/6 regulatory network.

Adhesion GPCR Latrophilin 3 regulates synaptic function of cone photoreceptors in a trans-synaptic manner

Cone photoreceptors mediate daylight vision in vertebrates. Changes in neurotransmitter release at cone synapses encode visual information and is subject to precise control by negative feedback from enigmatic horizontal cells. However, the mechanisms that orchestrate this modulation are poorly understood due to a virtually unknown landscape of molecular players. Here, we report a molecular player operating selectively at cone synapses that modulates effects of horizontal cells on synaptic release. Using an unbiased proteomic screen, we identified an adhesion GPCR Latrophilin3 (LPHN3) in horizontal cell dendrites that engages in transsynaptic control of cones. We detected and characterized a prominent splice isoform of LPHN3 that excludes a element with inhibitory influence on transsynaptic interactions. A gain-of-function mouse model specifically routing LPHN3 splicing to this isoform but not knockout of LPHN3 diminished Ca_V1.4 calcium channel activity profoundly disrupted synaptic release by cones and resulted in synaptic transmission deficits. These findings offer molecular insight into horizontal cell modulation on cone synaptic function and more broadly demonstrate the importance of alternative splicing in adhesion GPCRs for their physiological function.

Mapping epigenetic divergence in the massive radiation of Lake Malawi cichlid fishes

Epigenetic variation modulates gene expression and can be heritable. However, knowledge of the contribution of epigenetic divergence to adaptive diversification in nature remains limited. The massive evolutionary radiation of Lake Malawi cichlid fishes displaying extensive phenotypic diversity despite extremely low sequence divergence is an excellent system to study the epigenomic contribution to adaptation. Here, we present a comparative genome-wide methylome and transcriptome study, focussing on liver and muscle tissues in phenotypically divergent cichlid species. In both tissues we find substantial methylome divergence among species. Differentially methylated regions (DMR), enriched in evolutionary young transposons, are associated with transcription changes of ecologically-relevant genes related to energy expenditure and lipid metabolism, pointing to a link between dietary ecology and methylome divergence. Unexpectedly, half of all species-specific DMRs are shared across tissues and are enriched in developmental genes, likely reflecting distinct epigenetic developmental programmes. Our study reveals substantial methylome divergence in closely-related cichlid fishes and represents a resource to study the role of epigenetics in species diversification.

Analysis of Homozygous-by-Descent (HBD) Segments for Purebred and Crossbred Pigs in Russia

Intensive selection raises the efficiency of pig farming considerably, but it also promotes the accumulation of homozygosity, which can lead to an increase in inbreeding and the accumulation of deleterious variation. The analysis of segments homozygous-by-descent (HBD) and non-HBD segments in purebred and crossbred pigs is of great interest. Research was carried out on 657 pigs, of which there were Large White (LW, n = 280), Landrace (LR, n = 218) and F1 female (♂LR × ♀LW) (F1, n = 159). Genotyping was performed using the GeneSeek^® GGP Porcine HD Genomic Profiler v1 (Illumina Inc., USA). To identify HBD segments and estimate autozygosity (inbreeding coefficient), we used the multiple HBD classes model. LW pigs exhibited 50,420 HBD segments, an average of 180 per animal; LR pigs exhibited 33,586 HBD segments, an average of 154 per animal; F1 pigs exhibited 21,068 HBD segments, an average of 132 per animal. The longest HBD segments in LW were presented in SSC1, SSC13 and SSC15; in LR, in SSC1; and in F1, in SSC15. In these segments, 3898 SNPs localized in 1252 genes were identified. These areas overlap with 441 QTLs (SSC1—238 QTLs; SSC13—101 QTLs; and SSC15—102 QTLs), including 174 QTLs for meat and carcass traits (84 QTLs—fatness), 127 QTLs for reproduction traits (100 QTLs—litter traits), 101 for production traits (69 QTLs—growth and 30 QTLs—feed intake), 21 QTLs for exterior traits (9 QTLs—conformation) and 18 QTLs for health traits (13 QTLs—blood parameters). Thirty SNPs were missense variants. Whilst estimating the potential for deleterious variation, six SNPs localized in the NEDD4, SEC11C, DCP1A, CCT8, PKP4 and TENM3 genes were identified, which may show deleterious variation. A high frequency of potential deleterious variation was noted for LR in DCP1A, and for LW in TENM3 and PKP4. In all cases, the genotype frequencies in F1 were intermediate between LR and LW. The findings presented in our work show the promise of genome scanning for HBD as a strategy for studying population history, identifying genomic regions and genes associated with important economic traits, as well as deleterious variation.

Teneurins: Mediators of Complex Neural Circuit Assembly in Mammals

The teneurins (Ten-m/Odz) are a family of evolutionarily ancient transmembrane molecules whose complex and multi-faceted roles in the generation of mammalian neural circuits are only beginning to be appreciated. In mammals there are four family members (Ten-m1-4). Initial expression studies in vertebrates revealed intriguing expression patterns in interconnected populations of neurons. These observations, together with biochemical and over-expression studies, led to the hypothesis that homophilic interactions between teneurins on afferent and target cells may help to guide the assembly of neural circuits. This review will focus on insights gained on teneurin function in vivo in mammals using mouse knockout models. These studies provide support for the hypothesis that homophilic interactions between teneurin molecules can guide the formation of neural connections with largely consistent results obtained in hippocampal and striatal circuits. Mapping changes obtained in the mouse visual pathway, however, suggest additional roles for these glycoproteins in the formation and specification of circuits which subserve binocular vision.